Inhibiting foaming of cellulose slurries containing wet strength resins



g 25, 1964 H. F. DONNELLY 3,146,158

INHIBITING FOAMING 0F CELLULOSE SLURRIES CONTAINING WET STRENGTH RESINS Filed April 50, 1962 This invention relates to the production of wet strength paper, to improved wet strength pulp suspensions having decreased foaming properties, and particularly to an improved process for the manufacture of wet strength paper with resins of cationic character wherein process efliciency is materially increased by effectively reducing the normal foaming propensities of such resins in pulp suspensions.

Surface-active agents very commonly tend to give strength and elasticity to films and to cause foam development and foam stability. Defoamers, contrarily, are employed to enter the bubble structure of unwanted foam and to upset the molecular arrangement occasioned by such surface-active agent; usually this foam-producing surface-active agent is an impurity but it may be a con stituent introduced for a specific purpose.

In the manufacture of wet strength paper for the production of tissue such as paper towels and the like, wet strength resins are utilized. Resins of cationic character have been found very effective for this purpose. These resins attach readily to cellulosic pulp fibers, which fibers themselves exhibit an anionic character. The effect of such combination is to produce, by the absorption of the resin by the cellulose, a cationically charged resin-fiber material.

In tissue paper production for use as toweling and the like, these cationic wet strength resins are fed in a dis persion of the fibers to the Wire pit of the paper machine; the suspension is then pumped from the pit to a pressure inlet of a forming wire and the resin-carrying pulp stock flows over the wire, forming a paper sheet. The resin, being attached to the fibers, is incorporated in the sheet.

In practice, however, a considerable quantity of fiber fines may pass through the wire and be returned to the Wire pit. Additionally, some longer fibers generally pass through the wire. The fines, however, are a stabilizing agent for any foam formation much as the impurity mentioned above; foam so stabilized is termed solids stabilized foam.

The cationic resins, particularly the polyamideepichlorohydrin resins, contained in a pulp suspension, tend to form foam when pumped and aerated. Pumping from the wire pit is generally necessary, and passage of the resin with the fines through the wire, on return to the pit, tends to cause further aeration. Thus, frequently, process con ditions are favorable for the development of foam. In fact, such foam may form to an extent that it forms a very large proportion of pit volume which is reduced on a temporary basis by sweeping the foam from the pit through an overflow with fresh water introduced into the pit; such is, of course, undesirable, since it dilutes the suspension unduly and particularly lowers the Wet strength resin concentration, reducing resin efficiency.

Additionally, foam formation occasions operating difficulties and an inferior product. One reason for this is that the fan pump efiiciency is materially lowered by the presence of air in the stock suspension. The fan pump which urges the pulp suspension from the pit to the wire is also subject to the passage of slugs of the foamed material, causing variations in fan pump pressure and variations in the flow of the pulp suspension to the wire. This results in uneven distribution of the fibers on the wire 3,l4fi,l58 Patented Aug. 25, 1964 and even the passage of slugs to the wire, thus resulting in an inferior sheet. In addition, these slugs affect the felts, shortening felt life, inhibiting drying of the sheet at machine speeds, and also deleteriously affecting the creping operation commonly employed in the manufacture of many tissue papers.

These cationic resins are desirable, however, for they permit the use of a pulp suspension system operating on the alkaline side and at close to the neutral points; also, the cost is low relatively for the polyamide-epichlorohydrin cationic resins, for example.

Commercially available antifoam agents or defoamers have been employed in these pulp-catoinic resin systems; oil type defoamers of themselves lack the desired eifectiveness and wire pit foam formation as well as foam formation in mix-wells and felt pits occurs excessively. Also, these oil type defoamers are hydrophobic and, if used in substantial quantity, tend to atfect bonding of the cellulosic fibers adversely as well as to affect creping operations by preventing proper release of the formed web from dryers.

It has now been found that the incorporation of small amounts of an anionic additive, such as the surfaceactive water-soluble hosphates, to a pulp-cationic wet strength resin-hydrophobic defoamer system is ideally suited, not only to prevent substantial foam formation with suppression of its accompanying undesirable results, but to secure additional benefits such as a reduction in cost and improved dry strength of the product in the sheet cross-direction and machine direction also.

The cost reduction achieved is due primarily to the fact that the presence of the surface-active phosphate reduces the amount of conventional defoamer required; improved strength is attributable, at least in some measure, to the fact that the reduced defoamer permits improved fiber bonding.

The extent of the reduction in the amount of conventional defoamer is dependent upon the particular hydrophobic defoamer employed with the surface-active phosphate; some defoamer is always required to be present, the anionic additive, if used alone, being relatively ineffective and, in fact, deleterious since it tends to react with the cationic resin, destroying paper wet strength efficiency. For this reason also the anionic additive is maintained at the minimum necessary quantity to effect foam inhibition without adversely affecting product properties.

It is believed that the successful use of an anionic additive in a system having a cationic resin wherein the resin is substantially unaffected by the additive for the intended purpose of the resin is quite unexpected. To achieve this desirable result, it has been found that the quantity of the anionic additive must be small relative to the resin but may exceed the quantity of conventional defoamer present.

One cationic resin employed in the pratice of the invention is an uncured, thermosetting resin comprising a Water-soluble polymeric reaction product of epichlorohydrin and a polyamide derived from a polyalkylene polyamine and a saturated dibasic carboxylic acid containing from about 3 to 10 carbon atoms. Resins of this type are described in United States Patent No. 2,926,116. Another is an uncured thermosetting alkylene polyaminepolyfunctional halohydrin resin type described in United States Patent No. 2,595,935. Resins of such nature are suitable for imparting wet strength to paper under neutral oralkaline conditions and may be employed in dilute aqueous suspensions of cellulosic fibers such as the suspensions employed in paper mills.

Suitable water dispersible defoamers or antifoam agents of the generally oleaginous or hydrophobic type useful in the invention are:

(a) The alcohols such as nonyl and octyl;

(b) Alcohols' in combination with high molecular weight (200-2000) polyalkylenes such as nonyl alcohol and polyoxyethylene;

(c) Glycerides such as glycerol monolaurate as well as triglycerides; and

(d) Esters of fatty acids and ethylene glycol such as diglycol laurate.

The preferred anionc agents are soluble polyphosphates, a most suitable one of which is sodium hexametaphosphate (NaPO this is water-soluble and apparently effective to exclude air from the fibers of the pulp suspension to an extent that the fibers sink in the pit and the fines, which sink also, are then not effective as stabilizers of foam. The small bubble formation due to air inclusion is normally reinforced by such fines and oil type defoamers are apparently relatively ineffective as penetrants. This inability of the defoamers to effect penetration of the foam is overcome when the hexametaphosphate is added to the suspension, whatever the exact mechanism involved.

The hexametaphosphate must be added to the suspension in such manner and such quantity that coprecipitation with the resin does not occur. For this reason it is desirable to add the anionic agent at a different point in the system than the cationic resin. Other soluble phosphates which are useful include sodium tetraphosphate and sodium tripolyphosphate (Na P O The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein the single figure illustrates one arrangement of equipment useful in the practice of the invention. The diagrammatic illustration shows one general arrangement of a pressure-forming or inlet type Fourdrinier papermaking machine; such machine is more fully described in United States Patent 2,756,629. Only sufiicient of the machine detail is shown herein to illustrate the practice of the invention. Other apparatus arrangements may, of course, be also utilized within the scope of this invention.

As shown, the Fourdrinier wire 11 is supported upon an open or suction type breast roll 13 and a couch roll 15; the wire is adapted to pass over a plurality of spaced table rolls 17 and suction boxes 19. The wire 11 is suitably tensioned by additional guide or tensioning means, as illustrated at 21.

A tray 23 which is adapted and arranged to collect the white water, that is, the liquid which drains through the wire during the web forming operation, is disposed within the upper and lower reaches of the wire 11, as indicated, and this tray discharges into mixing tank 25. Tank 25 is, as shown, about three-fourths filled.

Fresh water for makeup purposes is commonly added to the mixing tank 25 through spray head 27; additional paper stock as necessary is added through header 29 in the form of a dilute fiber suspension. In the practice of this invention, as described hereinafter, the cationic wet strength resin is added with the pulp suspension through header 29, and the anionic, water-soluble agent is added With the Water through spray head 27. The hydrophobic defoamer may be added, if desired, through spray head 27 with the anionic agent.

If desired, the separate spray heads as at 30 may be employed to provide the water-soluble anionic agent with the defoamer, the agent being provided in water solution and water only being added through spray head 27. However, the spray heads 27 or 30, when supplying the anionic agent, should be directed to the Wire pit surface and at a point remote from the introduction of the cationic resinpulp suspension, and preferably also at a point remote from the discharge of tray 23 into tank 25. Such arrangement minimizes the tendency of the cationic resin and anionic agent to interact.

The bottom of the mixing tank 25 is inclined, as shown, and a main flow line 31 connects to the tank at the lower tank end. The main flow line 31 includes a branch extension 33 having a valve 34 therein for use in draining the mixing tank; the main flow line 31 also connects with the inflow side of a stock or fan pump 35. Pump 35 is the principal means upon which reliance is placed to deliver stock to the web-forming or wire 11 region of the machine.

The outletof pump 35 is connected to the inlet structure of the papermaking machine by piping indicated at 37. Such piping includes an automatically operable pressure regulating valve 39, a transition section 41 which converts the circular cross-sectional stream delivered by the pump 35 to a stream of rectangular outline, and a flow spreader 43. The flow spreader 43 converts the uniformly dimensioned stream delivered by the section 41 into a relatively shallow stream of rectangular cross-section which desirably has a transverse width substantially equal to the cross-machine width of the web-forming region or Wire 11.

An angle connection 44 anda conduit 45 connect the outlet end of How spreader 43 to the wire region 11. Conduit 45 is provided in the flow control unit designated generally at 47 which is itself attached to the machine frame 85. The flow connections 44 and 45 are each also rectangular in section and of the same cross-sectional dimensions as the outlet end of the spreader 43.

Included in piping 37 is a by-pass line 51 which connects the outlet side of the fanpump 35, upstream of valve 39, with the mixing tank 25. Included in by-pass line 51 is a shut-off valve 53.

Showers or spray heads 55 are provided to effect con- ,tinuous cleaning of the rolls and wire; such spray heads 55 may distribute the anionic agent also.

In usual web-forming operation, the dilute aqueous fiber suspension is pumped from the tank to the wire 11, valves 35 and 53 being closed. The suspension spreads out in ,a thin film on the wire 11 in the usual manner of forming a paper Web, water, and, on occasion, some fines draining to the tray 23 and back to the tank 25.

In the production of webs having wet strength, cationic resins, as already noted, are frequently employed. Such resins are water-soluble and customarily added to the paper pulp suspension prior to delivery of the suspension to tank 25, which delivery is through the inlet pipe or header 29. This delivery rate is governed as to volume and fiber concentration in relation to the water addition through heads 27 and 30 to assure a dilution of the fiber slurry to about 0.5% fiber by weight as the fiber passes to the screen. The fiber slurry entering through header 29 may contain as much as 3% fiber by weight; the mode of balancing the input and output may be effected in any convenient manner and is not further described since it forms no part of the present invention.

The cationic resins tend, however, to foam and, on occasion, tank 25 contains foam to the extent that a sweeping out is necessary; also, on occasion tank 25 simply spills foam over its top. Fines passing through the wire tend to stabilize such foam and appear to encourage both its stability and volume rise. This results in a material buildup of fiber in the pit as well as other disadvantages noted hereinbefore.

Antifoam agents, such as discussed hereinbefore, when employed in the aqueous system tend to reduce such foam but are relatively ineffective.

As illustrated by the following examples, the addition of anionic surface active agents in controlled quantity, and particularly sodium hexametaphosphate, suppresses such foam formation if the anionic agent is employed with a hydrophobic defoamer.

Example I With the equipment of FIG. 1 in operation and tank 25 containing a suspension comprising an aqueous pulp suspension and including a cationic resin, foam developed in tank 25 and covered the surface of the liquid 26 to a depth of about 18 inches.

The pulp suspension was fed to the tank through header 29; the suspension as fed to the tank contained 3% by weight of pulp (dry basis), 0.03% by weight of wet strength resin (a Water-soluble cationic polyamide-epichlorohydrin), the balance being water to the extent of 97% by weight. The pulp itself is conventional for the purpose-50% sulfate, 40% sulfite, and by weight of groundwood. Dilution of the pulp suspension was effected by additions of Water to the pit through spray head 27. The suspension passing to the Wire is diluted to about 0.5% by weight pulp solids (dry basis).

The wet strength resin was initially added to the pulp as a 10% by weight aqueous solution having a pH of about 5. The suspension itself after resin addition had a pH of about 7.4.

As noted, this suspension foamed considerably. The foam included fiber fines in heavy concentration dispersed throughout the froth. The foam bubbles themselves varied in size but were relatively small. Agglomerates of fiber are clearly visible in the bubbles, the fiber fines stabilizing the foam. This foaming is not materially alleviated by the addition of a conventional hydrophobic defoamer-for example, diglycol laurate. The defoamer is initially added with the water through spray head 27 at a rate of about 3 pounds per ton of pulp fiber (dry basis weight). The temperature of the suspension is usually between 75 and 90 F. as is the additive. Such defoamer addition has substantially no beneficial effect in decreasing the foaming for commercial operation. Similarly, simply increasing the concentration of the defoamer had no material effect other than a slight decrease in foam volume.

However, by adding 9 pounds per ton of fiber (dry basis weight) of sodium hexametaphosphate With the defoamer concentration as above (3 pounds per ton of fiber or 0.15%) and water through spray head 27, the foam in the Wire pit was virtually eliminated.

Further, it was necessary to continue adding the combination of defoamer and hexametaphosphate to maintain the condition of foam elimination, that is, the treatment is a continuing one.

The quantity of wet strength resin is usually about 1% by weight based on the dry weight of the fiber; concentrations of 0.15% to 2% are effective, depending upon the particular result desired.

The breaking and substantial disappearance of the foam permitted fines to disperse and sink, and to be recirculated to the Wire; the pressure at the inlet to the wire increases temporarily rather considerably upon sodium hexametaphosphate addition. In the specific instance described the pressure increase was from about 100 to about 120 inches of mercury. This pressure drops back to 100 inches, however, as the system steadies; substantially constant pressure is then maintained as the development of pulp slugs, etc. is prevented.

Resin coagulation by contact of the resin and the sodium hexametaphosphate is inhibited by providing that the entry of the resin and hexametaphosphate to the system is physically Well spaced. Under such condition the cationic resin and anionic agent are well dispersed and of low concentration when in contact, thus preventing coagulation. Coagulation would not only destroy wet strength properties in the sheet but such coagulated resin might be picked up by paper machine wires or felts, filling the same and thus requiring more felt cleaning and prob ably shortened wire and felt life. Such is avoided by controlling the quantity and concentration of the hexametaphosphate relative to the resin.

' Example 11 The procedure is as in Example I except that the sodium hexametaphosphate is reduced to 7.4 pounds per ton (0.37%) and the defoamer addition is 4 pounds per ton of fiber or 0.2% (dry basis weight).

It is to be noted that overdoses of the defoamer alone were not only ineffective to prevent foam but decreased the tendency of the pulp fibers to bond together in the sheet forming on the wire. In contrast, the combined defoamer and anionic agent not only exerted an apparent synergistic effect, killing the foam, but also the fiber bonding was improved as to dry machine direction and crossdirection strength.

Example III The procedure of Example I is repeated except that: the oil type defoamer employed is a combination of nonyl alcohol and a high molecular weight polyoxyethylene and polyoxypropylene, the alcohol constituting about by weight of the defoamer and the balance being the oxyalkylenes. The sodium hexametaphosphate required in this instance is materially lessenedabout pound per ton of dry fiber (0.03%).with about 1 pound per ton (0.05%) of the defoamer per ton of dry fiber- In this instance the effect of an overdose of the defoamer on fiber bonding was not particularly detrimental to fiber bonding.

Example IV The procedure of Example I is repeated using octyl ing combination. The alcohol may be present to the extent of 5 pounds per ton of dry fiber (0.2%) with the hexametaphosphate present to the extent of 1 pound per ton (0.05%) of dry fiber. Again foam decreases with little or no adverse effect on fiber bonding.

In the foregoing examples the anionic agent may be other active inorganic soluble phosphates such as Na P O the activity, however, is most pronounced with sodium hexametaphosphate.

The addition of as little as 0.05% by weight of the sodium hexametaphosphate, based on the weight of fiber present, has been found to be eifective in reducing foam without reducing the wet strength efiiciency of the cationic resin. Simple trial and error tests will indicate the minimum effective concentration with any particular defoamer. Further, adding the anionic agent in well dispersed form is desirable to prevent deleterious local action. As little as 0.03% of the soluble polyphosphate is eifective but above about 1% the concentration is sufiicient to affect the wet strength of the product.

Even the minimum concentration of sodium hexametaphosphate permits cost reduction due to the reduction of oil type defoamer required. Additionally, bonding of the fibers in the sheet is improved because of the olfsetting of the de-bonding tendency of excess oil type defoaming agent.

The hydrophobic defoamer may vary widely in concentration and specific character but should be at least about 0.05% by weight on the basis of the dry fiber and tests indicate the upper limit should not exceed 2%. As already noted, the defoamer should be held to a minimum to achieve optimum cost reduction.

The addition of the anionic surface active agent in combination with an oil type defoamer is equally effective when added to other paper machine areas-that is, the felt pits, mix-wells, and the like where foaming tends to occur in quantity but to a lesser degree than when stabilized by fiber fines.

It will be understood that the fibrous web formed on the wire is itself treated in conventional fashion, the thermosetting resin being heat cured on dryers of the paper machine as water is driven from the web by the dryers.

The paper product is'itself slightly improved as to strength characteristics apparently due to the materially reduced quantity of oleaginous defoamer useful in the procedure.

By hydrophobic, oil type, or oleaginous defoamer in the specification and the appended claims is meant a defoamer which is dispersible or has very little solubility in aqueous media but which has a molecular arrangement such that it is materially soluble in organic solvents.

Coagulation of the wet strength resin results in decrease of wet strength properties of the paper; by reference to the concentration of the anionic surface active agent as insufficient to substantially coagulate the wet strength resin it is meant that the wet strength resin is not removed from areas of desired activity on the fibers to an extent sufficient =to significantly diminish Wet strength properties in the product.

It will be understood that this invention is susceptible to modification in order to adapt to diflerent usages and conditions and, accordingly, it is desired to comprehend such modifications within the invention as may fall within the scope of the appended claims.

What is claimed is:

1. The process of inhibiting foaming of an aqueous suspension of cellulosic pulp containing a water-dispersible, cationic, wet strength, thermosetting, alkaline curing but uncured resin' in an amount to render the pulp fibers cationically active and which uncured resin in aqueous suspension has a tendency to cause foam when the suspension is aerated, said process comprising circulating the suspension in a papermaking process in such manner that the suspension is exposed to air and necessarily aerated, and adding to the circulating suspension a hydrophobic defoamer to the extent of between about 0.05% and 2% on the dry weight of the cellulosic pulp and a water-soluble inorganic anionic polyphosphate in sufficient amount to suppress foam formation but insufficient in amount to substantially coagulate the wet strength resin on the fibers.

2. The process of inhibiting foaming of an aqueous suspension of cellulosic pulp containing a water-dispersible, cationic, wet strength, thermosetting, alkaline curing but uncured resin in an amount to render the pulp fibers 0 C3 cationically active and which uncured resin in aqueous suspension has a tendency to cause foam when the suspension is aerated, said process comprising circulating the suspension in a papermaking process in such manner that the suspension is exposed to air and necessarily aerated,-and adding to the circulating suspension a hydrophobic defoamer to the extent of between 0.05% and 2% on the dry weight of the cellulosic pulp; and a watersoluble inorganic anionic polyphosphate to the extent of between about 0.05 to about 1.0% on the dry weight of the cellulosic pulp, said polyphosphate quantity being insufficient to substantially coagulate the wet strength resin on the fibers.

3. The process of inhibiting foaming of aqueous alkaline suspensions of cellulose pulp containing a waterdispersible, cationic, wet strength, thermosetting, alkaline curing but uncured resin in an amount to render the pulp fibers cationically active and which uncured resin in aqueous suspension has a tendency to cause foam when the suspension is aerated, said process comprising circulating the suspension in a papermaking process in such manner that the suspension is exposed to air and necessarily aerated, and adding to the circulating suspension a hydrophobic defoamer to the extent of between about 0.05 and 2% on the dry weight of the cellulose pulp and sodium hexametaphosphate to the extent of between about 0.05% to about 1.0% on the dry weight of the cellulose pulp whereby said foam is suppressed without coagulation of the wet strength resin on the pulp fibers.

References Cited in the file of this patent UNITED STATES PATENTS 2,097,121 Fromm Oct. 26, 1937 2,723,959 Jacoby et al Nov. 15, 1955 2,753,309 Figdor July 3, 1956 2,797,198 Chappell June 25, 1957 2,893,883 Stephan July 7, 1959 2,926,116 Keim Feb. 23, 1960 FOREIGN PATENTS 1,102,546 Germany Mar. 16, 1961 1,101,935 Germany Mar. 9, 1961 

1. THE PROCESS OF INHIBITING FOAMING OF AN AQUEOUS SUSPENSION OF CELLULOSIC PULP CONTAINING A WATER-DISPERSIBLE, CATIONIC, WET STRENGTH, THERMOSETTING, ALKALINE CURING BUT UNCURED RESIN IN AN AMOUNT TO RENDER THE PULP FIBERS CATIONICALLY ACTIVE AND WHICH UNCURED RESIN IN AQUEOUS SUSPENSION HAS A TENDENCY TO CAUSE FOAM WHEN THE SUSPENSION IS AERATED, SAID PROCESS COMPRISING CIRCULATING THE SUSPENSION IN A PAPERMAKING PROCESS IN SUCH MANNER THAT THE SUSPENSION IS EXPOSED TO AIR AND NECESSARILY AERATED, AND ADDING TO THE CIRCULATING SUSPENSION A HYDROPHOBIC DEFOAMER TO THE EXTENT OF BETWEEN ABOUT 0.05% AND 2% ON THE DRY WEIGHT OF THE CELLULOSIC PULP AND A WATER-SOLUBLE INORGANIC ANIONIC POLYPHOSPHATE IN SUFFICIENT AMOUNT TO SUPPRESS FOAM FORMATION BUT INSUFFICIENT IN AMOUNT TO SUBSTANTIALLY COAGULATE THE WET STRENGTH RESIN ON THE FIBERS. 